To make pudding:
Mix corn starch, salt, 1 cup milk, egg yolks and vanilla with a wire wisk and set aside.
Heat 3 cups milk, butter and sugar until scalding, stirring constanty. Add cornstarch mixture to hot milk while stirring with whisk. Cook until thickened. Remove from heat before boiling. Stir in chocolate chips while the mixture is still hot.
Place pudding in refridgerator to chill. Stir every 10 minutes.
To make crumbs:
Mix powdered sugar, cocoa, and peanut butter until small crumbs form (with mixer).
Place ½ crumbs into pie shell. Spoon pudding onto crumbs. Place remaining crumbs on top of pudding, reserving a little for the topping. Top with whipped cream (homemade is best, but cool whip will work).